Field of the Invention
The present invention relates to an image forming system.
Discussion of the Background
When a large amount of recording sheets are discharged from an image forming apparatus, the recording sheets become bulky and unstably discharged. Consequently, alignment of the recording sheets stacked on a discharge tray is degraded significantly, which has conventionally resulted in problems. For example, sorted portions of the recording sheets may be difficult to recognize. A jam may be caused at the time of discharging the recording sheets. The recording sheets may fall off the discharge tray. In order to stabilize alignment of a stack of recording sheets, there has been proposed an image forming apparatus to sheaf recording sheets by a predetermined number of sheets and discharge a sheaf of the recording sheets. Similarly, there has been proposed a post-processor attached to an image forming apparatus to accommodate recording sheets in a stack tray of the post-processor before a stack of the recording sheets are discharged to the discharge tray. From the stack tray, the recording sheets are sheafed by a predetermined number of sheets and discharged. A decrease in productivity of such a post-processor due to sheafing discharge should be prevented even in the case of sheafing discharge of the recording sheets. For this purpose, the post-processor executes the following control. A succeeding recording sheet is conveyed at the same recording sheet conveyance interval as normal conveyance, and conveyance of a preceding recording sheet is stopped, or the preceding recording sheet is sidetracked to a separate sidetracking path. At a conveyance timing of the succeeding recording sheet, the preceding recording sheet and the succeeding recording sheet are superposed and discharged.
In the above-described control method, there is a case in which the preceding recording sheet on which the succeeding recording sheet is superposed is a recording sheet of a specified kind unsuitable to superposition. Examples of the recording sheet of the specified kind include a thick sheet, a folded recording sheet, or a recording sheet having a surface subjected to particular processing. When a recording sheet of such a specified kind is the preceding recording sheet, problems occur at the time of switching back the preceding recording sheet prior to sidetracking or at the time of superposition of the succeeding recording sheet on the preceding recording sheet. For example, separation and slip of conveyance rollers may unfortunately cause misalignment of folded portions, multiple folding, damage to the recording sheet, and defective conveyance.
In order to solve the above-described problems, as disclosed in Japanese Patent No. 5036632 and Japanese Unexamined Patent Application Publication No. 2011-105503, a post-processor includes a first conveyance path and a second conveyance path. The first conveyance path conveys recording sheets of a non-specified kind. A pre-stack portion is disposed on the first conveyance path. The second conveyance path conveys recording sheets of a specified kind and communicates with the first conveyance path on the downstream side of the pre-stack portion. The recording sheets are superposed and conveyed on the downstream side of these conveyance paths.
However, in such a configuration as disclosed in Japanese Patent No. 5036632 and Japanese Unexamined Patent Application Publication No. 2011-105503, the conveyance path to convey recording sheets of the specified kind is required for exclusive use. Consequently, it is necessary to provide a plurality of conveyance paths. This enlarges the apparatus and increases the number of component parts, which causes an increase in the cost.
The present invention has been made to solve the above-described problems. It is a technical object of the present invention to provide an image forming system that prevents enlargement of the apparatus and an increase in the number of component parts. Even in the case of a printing job including recording sheets of a specified kind, the image forming system stabilizes alignment of the recording sheets when discharged.